It is known to label a container, such as a bottle or a package, with a label.
Also known are printing systems that apply individualized marks or other information on a container with ink jet printers in ways that are not permitted by label printing. Such printing systems work in monochrome and are restricted to a few printing dots or lines.
Also known are wide print heads that can print widths of up to 174 mm per print head using print heads of different manufacturers. These print heads also work in monochrome.
To print in multiple colors, it is known to use several of these monochrome print heads, one for each color. These monochrome print heads are arranged one after the other and are offset to achieve an even pitch between individual printing dots. On a machine having a plurality of print heads arranged one after the other in a fixed manner, the pitch can be adjusted. In these machines, containers to be printed upon move past the print heads with constant speed. The number of containers that can be printed on per unit time by such a machine therefore depends on the printing speed of a print head.
Machines along the lines of the foregoing are practical for printing on absorbent packaging materials. However, if one wishes to print on a non-absorbent material, such as metal, glass or plastic, the ink typically has to cure between colors. Known ways to cure ink involve using heat to dry the ink, or using UV or electron beams to cause cross-linking in the ink. The need to cure the ink of one color before printing the next color means that the monochrome print heads can no longer be right next to each other. This is because curing stations must now be provided. This increases the length of such machines. If one wishes to increase the number of containers printed upon per unit time, either a plurality of printing systems have to be connected in parallel, or a different arrangement has to be selected.
The prior art also suggests arranging holders on a carousel, placing a container in each holder, and guiding the container along a circular path past print heads. A disadvantage of this is that it becomes difficult to cure the individual inks because one cannot insert an intermediate drying or cross-linking station.
Another known device features individual carousels arranged one after the other in series. Curing takes place during the transfer between adjacent carousels. These embodiments feature holding devices to clamp the containers in a centered position on corresponding independent transport units. A belt moves the holding devices, and hence the containers, one after the other through the series of carousels. Each holding device has a rotary mounting so that the entire surface of the container can be exposed to the print head. Also known is having a marking on each holding device to mark the zero-degree angle.
The requirements of centering and maintaining the accuracy of the guide for achieving a high-quality print image, however, are high. Doing so is a complex undertaking impeded by several physical constraints. For example, during start-up and braking, different tensile forces act on the belt. There can also be temperature fluctuations that cause expansion or contraction. Both of these effects can lead to tolerances being exceeded to the point where they cannot be compensated for.
To make matters worse, the container can sometimes be quite heavy. For example, when the container is a bottle, the printing normally takes place after the bottle has been filled. Added to this weight is the mass of the holding device itself. Moving heavy objects with great precision is often difficult.
The precision of the centering requirement is quite high. For example, when printing at the usual 600 dpi, the printing dots are 0.042 mm apart from one another. It is very hard to reliably align a holding device that is holding a rather heavy bottle filled with liquid to within 1/100 mm.
Additionally, the wear and tear on a commercial printing machine is very high. A printing machine used in the beverage industry can typically process 36,000 bottles/hour. This means that more than 200,000,000 annually pass through such a machine. Because of this, the wear on the machine is huge, and substantially influences the printing quality.